The present invention is directed to evaluation of a data line to determine whether a load on the data line is appropriate for powering using the data line. Some equipment is configured to accept operating power from an attached data line over which data is received. Such data line-provided power is appropriate for certain loads, such as resistive loads, but is not appropriate for other loads, such as capacitive loads. Certain industry standards set forth criteria by which it may be determined whether a device attached to a data line is an appropriate device for powering using the data line. By way of example and not by way of limitation, an exemplary industry standard allows powering a load (i.e., a device) in an Ethernet system when the load is measured within tolerances of 25 KΩ.
A problem exists, however, when the load is in the nature of a capacitive load. Multiple attempts to power a capacitive load may cause the load to charge and eventually reach a charge level where the load appears to be a 25 KΩ load. A system looking for a qualifying impedance level (e.g., 25 KΩ) may erroneously power such a charged capacitive load and may damage the powered device. When power-level signals are provided to logic-level circuitry, the logic-level circuitry may be damaged or destroyed.
There is a need for a method and apparatus for characterizing a load on a data line that can distinguish among load-types.
In particular, there is a need for a method and apparatus for characterizing a load on a data line that can distinguish between resistive loads and non-resistive loads.